A jet engine of an aircraft includes a fan to take air therein, a compressor to take in and compress part of the air taken by the fan, a combustor to mix compressed air generated by the compressor with fuel and to combust the mixture, and a turbine to drive the fan and the compressor by using combustion gas from the combustor, which are all arranged in sequence.
The compressor, combustor and turbine are installed in a main nozzle as a cylindrical partition, and the fan is placed in the upstream side of the main nozzle. Most of the air taken by the fan flows through a bypass flow path provided between the main nozzle and a casing covering the outer periphery of the main nozzle. The air (a bypass flow) which has flowed through the bypass flow path is exhausted so as to surround the outside of a core flow (a jet flow) of the turbine, and thus joins to the jet flow.
The area where the jet flow and the bypass flow join to each other becomes a noise source, and thus noise occurs. Various arts are disclosed to reduce such noise.
For example, an art is disclosed in which the trailing edge perimeter of the bypass flow path of the casing (an engine nacelle) and the trailing edge perimeter of a jet flow path of the main nozzle are formed as saw-teeth shape, which is called a Chevron a Nozzle. A fluid which flows in the inner periphery side of the main nozzle and a fluid which flows in the outer periphery side thereof are efficiently mixed, and thereby the noise is reduced (e.g., refer to Patent Document 1).
In Patent Document 2, a system and a method are disclosed to reduce exhaust noise of a jet engine nozzle having projections (Chevron). The method disclosed in Patent Document 2 includes steps of generating a first flow of gas by a jet engine, delivering the first flow through a nozzle having a trailing edge perimeter that includes multiple projections extending in the aft direction, and injecting a second flow of a pressurized fluid into the first flow proximate to the projections.
In Patent Document 3, a device is disclosed to reduce exhaust noise of a jet engine by using an oscillating jet.
In addition, an art is disclosed in which a plurality of pipes that communicate with a fan section or the compressor is installed around the main nozzle, and the tip of each of the pipes is configured as a nozzle to inject part of compressed air (e.g., refer to Non-Patent Document 1). The nozzle configured in this way injects a microjet to the confluence of the jet flow and the bypass flow. According to this, the jet flow and the bypass flow are properly mixed by the swirl generated by the microjet, and noise can be reduced further.